Allow jumping ahead by 100, 500, or even 1000 images.
Some artists or categories have 100's or even 1000's of images. Yet, you only allow the user to move ahead 20 images at a time. For instance, your "Surrealism" category contains 6000+ images. If I can only progress by 20 images at a time, I will NEVER reach the end. Please allow the user to take bigger "jumps" in such cases. Thanks !!